In particular, in the oil & gas industry, it is known to create permanent underwater facilities for the extraction and/or production of hydrocarbons from wells drilled in the bed of a body of water. Within the scope of this description, the term “permanent” means underwater facilities intended to operate on the bed of a body water for an indefinite number of years. In the description that follows, the term “hydrocarbon production” means the extraction of hydrocarbons, the processing of hydrocarbons, the treatment of fluids related to hydrocarbon production and the subsequent transport.
Underwater hydrocarbon production facilities can be placed at or relatively close to subsea wells or in intermediate locations, and can have various configurations on the bed of a body water depending on the well or well field. In addition, underwater hydrocarbon production facilities can be positioned in relatively shallow water or in relatively very deep water and in any geographic area, independently of whether environmental conditions are mild or extreme.
The concept of an underwater hydrocarbon production facility was developed by operators in the industry with the objective of rationalizing hydrocarbon production from subsea wells. In short, an underwater hydrocarbon production facility is part of a complex installation that comprises an underwater hydrocarbon production facility and pipelines for relatively long-distance transportation between underwater facilities and surface structures. The exploitation of subsea oil and/or gas fields via underwater hydrocarbon production facilities that provide for the extraction and transport of the hydrocarbon to the surface or coast has been under way for some time and expansion in the near future is foreseeable. Recent technological developments in underwater devices suitable for working at relatively great depths and the great interest of oil companies have facilitated the feasibility of relatively complex systems, broadened the potentiality of underwater production facilities and made any type of active process in water possible. The main underwater treatment processes are: fluid pumping or compression, multiphase pumping, liquid/liquid separation, gas/liquid separation, solid/liquid separation, oil/water/gas separation, treatment and pumping, water treatment, heat exchange, and injection of water or gas into the well.
Further information on the current state of underwater hydrocarbon production facilities are available in the document OTC 24307 “STEPS TO THE SUBSEA FACTORY” by Rune Ramberg (Statoil), Simon RH Davies (Statoil), Hege Rognoe (Statoil), and Ole Oekland (Statoil).
There is no doubt that underwater hydrocarbon production facilities provide numerous advantages, but the construction, maintenance and control of an underwater hydrocarbon production facility are beset by problems that grow as the depth and/or environmental constraints increase.
In particular, the maintenance and inspection of underwater facilities is currently carried out by unmanned underwater vehicles, which comprise two distinct types of vehicle: ROVs (Remoted Operated Vehicle), each of which is connected to a base station by an umbilical cable, through which ROV receives power and exchanges signals, and AUVs (Automated Underwater Vehicle), each of which has an autonomous power source and is configured to operate on the basis of predefined programs and to upload any information collected in the operational phase once AUV returns to the base station. U.S. Published Patent Application No. 2002/0040783, PCT Patent Application No. WO 2015/061600, U.S. Pat. No. 6,390,012 and PCT Patent Application No. WO 2015/124938 illustrate underwater vehicles and/or maintenance and inspection systems for underwater facilities that employ underwater vehicles of the above-indicated type. Known systems generally use only one type underwater vehicle, with the consequent operating limits, or different types of underwater vehicles, but to the detriment of operating costs. The above-mentioned solutions are completely or partially ineffective, especially where the environmental conditions or the facility's configuration make the support they need from surface vessels economically or technically impracticable.